Method of restoring formation permeability

ABSTRACT

A method for restoring original permeability to a subterranean oil producing formation penetrated by a well. The method includes the steps of injecting into the formation a slug of pressurized gasiform fluid, then a slug of aqueous silicate solution, retaining the solution in the formation for 2- 24 hours, then removing the solution by the force of the pressurized fluid. These steps accomplish dispersal of clay particles blocking formation permeability and restoration of the formation&#39;&#39;s original permeability.

William G. Halbert Butte, Mont.

Jan. 15, 1970 May 1 1, 197 l Tenneco Oil Company Houston, Tex.

lnventor Appl. No. Filed Patented Assignee METHOD OF RESTORING FORMATIONPERMEABILITY 5 Claims, No Drawings References Cited UNYTED STATESPATENTS Joosten 1/ 1943 Campbell Primary Examiner-Stephen J NovosadAtt0rneysEugene S. Coddou and Lee R. Larkin ABSTRACT: A method forrestoring original permeability to a subterranean oil producingformation penetrated by a well. The method includes the steps ofinjecting into the formation a slug of pressurized gasiform fluid, thena slug of aqueous silicate solution, retaining the solution in theformation for 2- 24 hours, then removing the solution by the force ofthe pressurized fluid. These steps accomplish dispersal of clayparticles blocking formation permeability and restoration of thefonnation's original permeability.

METHOD OF RESTORING FORMATION PERMEABILITY BACKGROUND OF THEINVENTION 1. Field of the Invention This invention generally relates toa method of restoring original permeability of a subsurface formationpenetrated by a well. More specifically, this invention relates to amethod of dispersing clay particles blocking the pores of a petroleumreservoir rock by injecting an aqueous solution containing a solublesilicate into the formation following an injection of pressurizedgasifonn fluid which provides driving power to expel the aqueoussolution from the formation.

2. Description of the Prior Art The problem of decreased permeabilityand decreased oil flow in a producing oil well has been recognized andmany attempts at solutions for this problem have been made. The nativeclay contained by most petroleum reservoir rocks become mobile duringproduction and tends to clog the area around the wellbore. The tinymobilized clay particles congregate around the rock's pore openings inso-called brush heaps." Prior art methods of acidizing and flushing withfresh water have given only temporary solutions to this-problem.

Rather than attempting to repair damage to the formation immediatelysurrounding to the'wellbore, the customary way of restoring permeabilityis to induce a fracture. This fracture is made to extend through thedamaged zone and into the undisturbed portion of the reservoir.Fracturing is very expensive and only partial success has been reported.

The method of attempting to repair damage to the formation onlyimmediately surrounding the wellbore has been attempted also. However,heretofore, only temporary relief has been obtained by injecting analien fluid such as certain alcohols or certain acids into a very smallarea immediately surrounding the wellbore. Although the expense ofattempting to affect the formation in a much wider area by fracturing isavoided by this method, it has been found that the clay will returnafter these acid or alcohol washings, and later will again obstruct theflow of oil to the well.

SUMMARY OF THE INVENTION An object of this invention is to provide animproved and economical method of restoring original permeability of asubsurface formation penetrated by well. More specifically, an object ofthis invention is to provide an improved method to disperse the clayparticles which block the pores of a petroleum reservoir.

The method of this invention for increasing permeability of a subsurfaceformation penetrated by a well includes the step of injecting into theformation a slug of gasiform pressurized fluid whereby the pressurizedfluid provides driving power to expel a subsequently injected fluid fromthe formation. It also includes the step of injecting into the formationa slug of aque ous silicate solution containing SiO and Na O in a weightratio in the range of about l.254.0 parts SiO to 1 part Na O and havingdissolved solid content of about 24 percent-36 percent by weight SiO and9 percent percent by weight Na O. The solution is retained in theformation for a period of about 2-24 hours, after which the solution isremoved from the formation by the driving power of the pressurizedgasiform fluid.

The preferred weight ratio of SiO to Na O is in the range of about1.8-2.5 pans SiO to 1 part Na O and the preferred dissolved solidscontent is in the range of about 24 percent- 26 percent by weight SiOand l l percent-l3 percent by weight Na O. In certain embodiments, it ispreferred that the size of the slug of aqueous silicate solution doesnot exceed about 4 percent of formation pore volume.

The method may also include the additional step of injecting a slug ofretarded hydrofluoric acid into the formation and subsequently removingit, whereby the siliceous material immediately surrounding the well isdissolved and carried away.

Certain embodiments of the invention may include the steps of injectinga slug of gasiform pressurized fluid prior to the in- LII jection andremoval of each slug of hydrofluoric acid and aqueous silicate solution,which gasiform injections provide driving power to expel the acid andthe silicate solution from the formation.

The size of each of the slugs of retarded hydrofluoric acid and silicatesolution preferably does not exceed about 4 percent of formation porevolume.

In carrying out one embodiment of this invention, an aqueous solutioncontaining soluble silicates is injected into the damaged zone. Thiscolloidal siliceous material is known to have a high surface activityand a high negative electrical charge. The soluble alkali silicate isreadily absorbed by clay, causing dispersion of the congregatedparticles. Having dispersed the clay, the particles are then availablefor flow into the wellbore or dissolution by hydrofluoric acid. Thisremobilization and removal of clay particles causes the restoration ofthe formation '5 permeability.

Many advantages have become apparent in the use of this method forrestoring permeability. The tiny clay particles which have agglomeratedaround the pore openings of the rocks in so-called brush heaps" can bedisaggregated by forcing each particle to assume a like negative charge.Like charges repel and adsorption of a like electrical charge by eachparticle will cause dispersion of the particles in the brush heap." Thedispersed or remobilized particles can be flowed out of the wellbore orcan be dissolved in situ by subsequent contact with an acid known todissolve clay.

One advantage of this invention over the prior art is that the clayparticles are actually removed from the formation in the areaimmediately surrounding the wellbore instead of only flushed backwardsinto the formation by the action of injected slugs of fresh water orcertain acids. Merely flushing the agglomerated clay particles back intothe formation to relieve temporary stoppage of flow only leaves theparticles free to again clog the area immediately surrounding thewellbore after a period of slightly increased flow. The presentinvention extracts the particles completely from the area surroundingthe wellbore. This innovation yields a longer lasting increasedpermeability at a substantially reduced cost from fracturing and a costslightly greater than short lived permeability restoration by injectionof fresh water and certain acids.

Alternate embodiments and further modifications to the process will beapparent to those skilled in the art in view of the description, whichis to be construed as illustrative only.

Iclaim:

I. In a method for increasing permeability of a subsurface formationpenetrated by a well, the combination of steps comprising:

* injecting a slug of gasiform pressurized fluid into said formation,whereby said pressurized fluid provides driving power to expel asubsequently injected fluid from said formation;

thereafter injecting into said formation a slug of aqueous silicatesolution containing SiO and Na O in a weight ratio in the range of aboutl.254.0 parts SiO to 1 part Na O, with said solution having a dissolvedsolids content of about 24 percent to 36 percent by weighting SiO, and 9percent to 20 percent by weight Na,0;

retaining said pressurized fluid and said silicate solution in saidformation for a period of about 2 to 24 hours;

and removing said solution from said formation by the driving power ofsaid slug of gasiform pressurized fluid.

2. The invention as claimed in claim 1 including the additional stepsof:

injecting a slug of gasiform pressurized fluid and then a slug ofretarded hydrofluoric acid into said formation and subsequently removingsaid acid slug to thereby dissolve and assist removal of siliceousmaterial from the area immediately surrounding said wellbore.

3. The invention as claimed in claim 2 wherein:

the size of each of said slugs of retarded hydrofluoric acid andsilicate solution does not exceed about 4 percent of formation porevolume.

4. The invention as claimed in claim I wherein.

the size of said slug of aqueous silicate solution is less than part NaO on a weight bas and d diss lved Solids nabout 4 percent of formationpore volume tent is in the range of about 24 percent to 26 percent by 5.The invention as claimed in claim 1 wherein: weight SiO v and l 1percent to 13 percent by weight said silicate solution contains about1.8-2.5 parts SiO to l Na O.

2. The invention as claimed in claim 1 including the additional stepsof: injecting a slug of gasiform pressurized fluid and then a slug ofretarded hydrofluoric acid into said formation and subsequently removingsaid acid slug to thereby dissolve and assist removal of siliceousmaterial from the area immediately surrounding said wellbore.
 3. Theinvention as claimed in claim 2 wherein: the size of each of said slugsof retarded hydrofluoric acid and silicate solution does not exceedabout 4 percent of formation pore volume.
 4. The invention as claimed inclaim 1 wherein: the size of said slug of aqueous silicate solution isless than about 4 percent of formation pore volume.
 5. The invention asclaimed in claim 1 wherein: said silicate solution contains about 1.8-2.5 parts SiO2 to 1 part Na2O on a weight basis, and said dissolvedsolids content is in the range of about 24 percent to 26 percent byweight SiO2 and 11 percent to 13 percent by weight Na2O.